SR-71 Blackbird
Successfully complete the Pilot bonus objective for the final mission (Mission 4.5: Final Count Down) to unlock the SR-71 Blackbird.

The Big One (SR-71 Blackbird Weapon Pack)
Successfully complete the Ace bonus objective for the final mission (Mission 4.5: Final Count Down) to unlock the SR-71 Blackbird's fourth weapon pack. This weapon pack includes the game's super weapon, the A-SLAMR. The A-SLAMR does not recharge once fired so use it wisely. Note: The SR-71 Blackbird and "The Big One" weapon pack can both be unlocked at the same time if playing on the Ace difficulty setting. Just complete both of the required bonus objectives to unlock the SR-71 and "The Big One" weapon pack together (instead of separately).